1. Lies about the process / promissary lies. e.g. "If you just confess, you can go home." 2. Lies about evidence. e.g. "We talked to {Friend|Family|Co-conspirator} and they said you did it and they have the {item} to prove it. It's not going to look good if you continue to lie to me."
#1 seems obviously bad to me. Too high of a risk of tricking innocent people into thinking they can end the stress by falsely confessing.
#2 seems less bad, possibly beneficial. There are other comments about how this can speed up interrogations by getting people who are guilty to think they've been caught and confess. I could be convinced otherwise.
In my opinion, sounds like 1 and 2 should be illegal for minors. But 1 should be illegal in general, for adults too.